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Problems with Extruder - Please help

Posted by demetris 
Problems with Extruder - Please help
January 26, 2013 10:03AM
Hello everyone,
Until this morning I was printing ok and I was calibrating away.
At some point my extruder started extruding only TINY amount of filament. For many hours I thought that was because of some settings I was changing in Slic3r. After I couldn't solve the problem whatever I changed in Slic3r, I thought that maybe the problem is something else.

I tried to print some gcodes that I had from yesterday (which printed just fine yesterday) and the problem is still there! I only see tiny blobs of filament on the glass. Nothing more. If I extrude manually though printrun it works just fine and for the correct length.

Note that I changed nothing in the firmware since yesterday so if I am correct gcodes from yesterday should still work fine.

Please let me know what you think as I am running out of ideas :/

Thank you

EDIT: I checked temperatures during printing and they do not drop

Edited 1 time(s). Last edit at 01/26/2013 10:05AM by demetris.
Re: Problems with Extruder - Please help
January 26, 2013 11:56AM
1. Make sure the small gear on the extruder is not slipping.
2. Check that you can push filament through by hand with little force. Make sure to loosen the ider completely.
3. If you cannot push easily, you probably have a backflow condition. This can happen if the tip was left hot for an extended period without printing.

What kind of hot end are you using?
Re: Problems with Extruder - Please help
January 26, 2013 05:55PM
Hi jcabrer and thanks for the reply.

I am using J-Head nozzle.

1-The small gear seems to work fine.
I will test what you suggest in 2 tomorrow. From what I remember I did left the nozzle hot for a while (half an hour maybe?). If it is indeed a backflow problem, how do you get it fixed?

Thank you!
Re: Problems with Extruder - Please help
January 27, 2013 11:14PM
OK. I use the J-Head hot end myself, although I have never experience the backflow problem there. This may be because I'm printing with ABS, which does not cause the problem as often as PLA.

Asuming this is your problem, let me first explain the what and why of it.

PLA and ABS are not just the print material. They are also part of the cooling system of the printer. You see, as you print, the filament take away a lot of the heat with it. Since the thermistor is regulating the temperature, the lost heat is quickly replaced, and we continue to print along. Because the flow of plastic is rather fast, most of the heat loss is in the direction of the nozzle during a print.

This is not true when the printer is idle. When you are not printing, the thermal wave travels up the hot end, albeit slowly, to the insulating tube, where it begins to warm the "cold" filament. With PLA in particular, this is a problem because PLA gets soft (glass transition) at fairly low temperatures, compared to ABS. If you start a print when the "cold" filament is in its glass transition range of temperature, the filament will collapse, rather than push down, and some of it will travel back up, to the cooler area of the tube, where it will again solidify.

At this point, you have to take your hot end apart, and clean out the components. Be very careful not to damage threads, or the nozzle. If you are printing with ABS, you can soak things in acetone to disolve the plastic. If it is PLA, you will need to warm things up, and try and remove as much material as possible. If you can remove the brass nozzle, you can heat it on a stove with a Vent Hood, and burn it clean. Drop it in water, to flash off any residue, while hot.
Re: Problems with Extruder - Please help
January 30, 2013 10:39PM
I have been having a similar problem. I was wondering if anyone new what g code could be entered into the splicer initial settings in order to give the extruded a good long purge right before it starts printing?
Anonymous User
Re: Problems with Extruder - Please help
January 30, 2013 11:30PM
maybe this?
M190 S70 ; wait for bed temperature to be reached
M104 S200 ; set temperature
G28 ; home all axes
M109 S200 ; wait for temperature to be reached
G90 ; use absolute coordinates
G21 ; set units to millimeters
G92 E0
M82 ; use absolute distances for extrusion
G1 F12000 ; set speed 200 mm/sec
G1 Z15 ; go up 15 mm
G1 F3000 ; set speed 50 mm/sec
G1 E20 ; extrude 20 mm
G4 P30000 ; wait 30 seconds
G1 F12000 ; set speed 200 mm/sec
G1 Z0 ; go back down
G92 E0 ; set extruder to 0 mm

Edited 1 time(s). Last edit at 01/30/2013 11:35PM by ohioplastics.
Re: Problems with Extruder - Please help
January 31, 2013 02:14AM
Simply activate the skirt / brim function in your slicer.

Bob Morrison
W├Ârth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse
Re: Problems with Extruder - Please help
January 31, 2013 06:40PM
Thanks, I had the brim turned on but it wasn't enough so I edited ohioplastics referaneced code to:

G28; home axes
G92 E0;
G1 E20; extrude 20 mm
G4 P10000; wait 10 seconds
G92 E0; set extruded to 0 mm

Now it dumps all the bubbles and continues on.
Re: Problems with Extruder - Please help
February 01, 2013 11:33AM
A fan blowing over your hotend is simply a must with pla to keep it cool before and during prints. It can be a very weak fan, even slight airflow is massively better than natural convection. I killed an old hotend (which was also a poor design) due to the ptfe ballooning because I didn't know this.
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